You’re a high school student living with your younger sister Aiko. Both your parents were killed in a accident leaving her as your only blood relative. She means the world to you, but recently, she says that she feels like someone is watching her. You brush it off as just her being a little too self-conscious… If only you knew what was to come...

One day, Aiko is late coming home from school. Worried, you head out to search for her and you find yourself at the door in mansion in the wood